Defective Microwave Photonic Crystals for Salinity Detection

Round 1

Reviewer 1 Report

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors of the manuscript titled "Defective microwave photonic crystals for salinity detection" present a numerical study where they demonstrate that by using one-dimensional defective photonic crystals it is possible to design salinity sensors. They demonstrate that the sensing capabilities can be optimized by optimizing the thickness of the stack. In addition, the defective resonance and transmission resonance have different properties and respond differently to different salt concentrations which make them suitable for sensing different ranges of salinity. 

While the idea of using photonic crystals has been explored extensively for different sensing applications including salinity sensing, in general this manuscript is well written and results are interesting because it reports results for microwaves. I therefore recommend publication of the manuscript after the authors address my following comments and questions : 

1. The authors show that by controlling the structure the sensing sensitivities can be changed. Did the authors perform any optimization studies ? Can an optimized structure ( thickness of stack and individual layers) be designed that the defective resonance can be used for sensing over a wide range of salinity ?
2. The manuscript has some typos and spelling mistakes. It requires some proof-reading. 
3. The authors use the Klein and Swift model for deriving the permittivities of saline solution. How accurate is this model for a broad range of saline concentration ?
4. How will the results change with change in temperature ? How sensitive/robust is the sensing technique to temperature fluctuations?  Currently it seems all the analyses have been done for 20oC. 
5. Is there any other material that may be better for designing these type of saline sensors at microwave frequencies?  

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Please check figure captions for Figures 4 and 5. Number of layers seems wrong in the captions. 

Figure captions would benefit from more information added to explain what is in the picture. e.g. Figure 1, more detail on the configuration and the layer structures. 

Abstract and Conclusions should contain some numerical results. 

Be clear throughout that all the results are from modelling. There are some phrases, such as "When the defective layer is filled with DI water (salinity 188
of zero)," which suggest experimental results. 

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript describes a salinity sensor based on a changing of peak  corresponding to the defect mode of a photonic crystal. The idea has been repeatedly demonstrated for sensors for other substances such as blood.

The novelty of the work is the use of the Klein and Swift model.

I have a number of comments to the authors:

1. What is first transmitting resonance. Perhaps you mean the peak corresponding to the first edge mode.
2.  Table 1 shows the Q factor for "first transmitting resonance". I believe that it is incorrect to call the edge of the band gap a resonance and find the Q factor for it.
3. The text does not contain a detailed description or references to a detailed description of the properties of Rogers 5880 and 6010 materials. 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have addressed all my comments and questions. I recommend publication of the manuscript. 

Reviewer 4 Report

The manuscript can be published in present form.